Engines may be configured to deliver fuel to an engine cylinder using one or more of port and direct injection. Port fuel direct injection (PFDI) engines are capable of leveraging both fuel injection systems. For example, at high engine loads, fuel may be directly injected into an engine cylinder via a direct injector, thereby leveraging the charge cooling properties of the direct injection (DI). At lower engine loads and at engine starts, fuel may be injected into an intake port of the engine cylinder via a port fuel injector, reducing particulate matter emissions. In addition, the NVH impact on the customer is reduced since the direct injectors and a high pressure fuel pump (HPP) delivering fuel to the direct injectors can make a ticking noise when active. During still other conditions, a portion of fuel may be delivered to the cylinder via the port injector while a remainder of the fuel is delivered to the cylinder via the direct injector.
During periods of engine operation where direct injection of fuel is disabled and no fuel is being released by the direct injector (e.g., during conditions where only port injection of fuel is scheduled), fuel trapped inside the DI fuel rail may expand due to high temperatures. This can result in a pressure build-up in the DI fuel rail as well as elevated injector tip temperatures. In addition, the temperature of the HPP may rise. If the deactivation period of the DI is long, the pressure and temperature build-up may be significant. Prolonged exposure to such high temperature and pressure conditions may cause internal damage to the fuel system components. To address this, while direct injection is disabled, fuel flow through the HPP and the DI system may be continuously adjusted based on an expected (e.g., modeled) HPP temperature to provide sufficient flow to cool the HPP without increasing ticking noise. One example method includes: during an engine warm idling condition, maintaining each of engine direct injectors and a high pressure fuel pump delivering fuel to the direct injectors disabled until a modeled temperature of the pump is higher than a threshold; and then temporarily reactivating each of the engine direct injectors and the high pressure fuel pump until the modeled temperature is below the threshold.
As an example, during warm idling, an engine may be fueled via port injection only. A DI injection system and the HPP delivering fuel to the direct injectors may be disabled. Responsive to a rise in modeled HPP temperature above a threshold, the HPP and the DI injectors may be intermittently enabled and fuel may be injected via DI at a flow rate through the HPP that provides sufficient cooling. This may be continued until the HPP temperature is below the threshold. Thereafter, both the HPP and the direct injectors may be disabled and only port injection of fuel may be resumed.
In this way, temperature control may be achieved at a HPP delivering fuel to a DI fuel rail, particularly during conditions of extended operation with only port fuel injection. The technical effect of maintaining a minimum fuel flow through the DI fuel system components is that the HPP may be cooled. By modeling the HPP temperature based fuel system conditions, the DI fuel flow may be better adjusted to maintain the HPP temperature in a desired range. By operating the HPP and the direct injector intermittently to maintain the HPP temperature below a threshold temperature, internal damage to the high pressure fuel pump is reduced. In addition, the HPP and direct injectors may be maintained deactivated for a longer duration, reducing the occurrence of ticking, and related NVH issues. Even when the direct injectors and HPP are intermittently activated for temperature relief, the amount of objectionable noise generated may be substantially lower, or negligible.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.